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Abstract

Nano-biological systems interfacing nano-structured solid surfaces with biological compounds such as oligonucleotides or proteins are highly regarded as enabling materials for biosensing and biocatalysis applications. In particular, nanostructures of noble metals such as gold or silver, when exposed to light, exhibit a phenomenon known as surface plasmon resonance. When a proper metal nanostructure (plasmonic substrate) is exposed to light, very efficient absorption of incoming photons is possible, resulting in a buildup of localized high-energy regions, or “hot-spots”, where energetic carriers or “hot carriers” can be created. These hot-carriers can be used to catalyze desired chemical transformations in materials located nearby. Furthermore, plasmonic hot-spots are also known to enhance inelastic scattering of light by the same materials, promising multi-functional applications that combine photo-catalytic stimulation of materials with their ultrasensitive characterization in the same design. In this thesis work, we developed a conjugate nano-biological system interfacing plasmonic gold nanostructures with thiolated single-stranded DNA carrying an important reduction-oxidation indicator, methylthioninium chloride, also known as methylene blue. Using surface-enhanced Raman spectroscopy, we have detected characteristic bands of DNA-bound immobilized methylene blue in sub-monolayer quantities. We also have detected reversible reduction-oxidation of methylene blue during laser excitation of the samples at neutral pH, in the absence of electrodes or chemical agents.